1. Technical Field
The present disclosure relates to a hybrid vehicle driving system that transmits power output by two types of power sources having different characteristics to wheels, a hybrid vehicle, and a driving method.
2. Description of Related Art
In recent years, a hybrid vehicle including two types of power sources having different characteristics has been put to practical use. The hybrid vehicle is configured so as to run with power output by the two types of power sources optimally combined depending on circumstances to make the most of advantages of the power sources and compensate for disadvantages thereof.
The conventional hybrid vehicle includes an internal combustion engine and an electric motor. Thus, for example, the internal combustion engine with low efficiency is stopped in a low speed or light load region and wheels are driven by the electric motor, thereby improving fuel efficiency.
However, the conventional hybrid vehicle has a problem that disadvantages of the internal combustion engine cannot be overcome such as high noise due to combustion and explosion of fuel, limitation on types of fuel, or difficulty in reducing exhaust gas containing pollutants.
The external combustion engine, unlike the internal combustion engine, lowers noise due to combustion, accepts a wide range of types and forms (gas, liquid, or solid) of fuel, and allows combustion under an optimum condition, and thus has an advantage of easily reducing exhaust of pollutants.
However, the external combustion engine has a disadvantage that a reaction rate of output adjustment is lower than that of the internal combustion engine.
Thus, an electric vehicle including an external combustion engine and an electric motor has been proposed (see Japanese Patent Application Laid-Open No. 2003-239804).
The electric vehicle described in Japanese Patent Application Laid-Open No. 2003-239804 is configured so that electric power generated by a generator interlocked with the external combustion engine is supplied to the electric motor, and power output by the electric motor is transmitted to wheels. In such an electric vehicle, the electric motor that is high in reaction rate of output adjustment drives the wheels, and the external combustion engine constantly drives the generator. Thus, there is no need for sudden output adjustment of the external combustion engine.